The invention relates to the field of manufacturing products having electronic circuit board and components, and more specifically, making a metallic contact for soldering the electronic components on the printed circuit board.
In all conventional soldering processes, three ingredients are required: flux which cleans surfaces, solder material, and heat to melt the solder. A solder connection or a metallic contact may be made by melting a solder alloy in contact with an electronic component termination coated with a metallic element. At the metallic contact, a metallurgical bond consisting of inter-metallic is then formed. Tight control during the soldering process is necessary because a detrimental inter-metallic condition could also form around the metallic contact depending on time/temperature (diffusion) conditions. Such detrimental inter-metallic conditions includes de-wetting and brittle solder joints. Thermal stress is induced within components, between components, and between component and printed circuit board because of the Coefficient of Thermal Expansion (CTE) mismatches during the temperature excursion of re-flow soldering, which may compromise product quality and reliability.
High-density electronic component assembly on a PCB usually requires re-flow of the solder compound. The small mass of electronic components makes them susceptible to the effects of surface tension of molten solder which could lead to soldering defects such as tombstone and unsolder conditions. To nullify surface tension effects, re-flowing the solder often occurs in an inert gas atmosphere which alters the liquid-gas interface leading to beneficial surface tensions. The most popular method of making electronic interconnections has been with eutectic or near-eutectic compositions of tin and lead. The technology is very mature with thorough understanding of processing, reliability, mechanical properties, electrical properties, and materials science. The eutectic composition for tin-lead is convenient because of its low cost and low melting temperature compared to other solders. The low melting temperature is important because high temperature processing places undesired stress on component packaging, substrates, printed circuit boards and also the material may degrade. Environmental concerns also have changed the soldering process over the years. Clean soldering is now a common requirement because of the concerns raised with ozone depleting solvents once used to remove flux from printed circuit boards. Lead-free soldering is also being evaluated as a means to minimize the hazards posed from disposal of electronic assemblies.
Therefore, there is a need for a soldering process that eliminates or minimizes the application of heat, and can also be used for lead free soldering.